It is sometimes necessary to install a three port two way check valve. One exemplary problem often occurs at storage tanks and oil fields. To set the background, several wells will be connected through gathering lines to a storage tank. The wells will flow into the storage tank through a common line. The tank will be filled and emptied through the common line. A pump will be installed in the common line, normally arranged to pump from the tank back into the common line when the tank is emptied. Thus, it becomes necessary to have bidirectional flow in the common line. Most pumps however cannot permit flow in both directions through the pump even when the pump is de-energized. The valve of the present invention is particularly useful in protecting the pump against reverse flow through it. Pumps of the impeller type, for instance, can only pump in one direction. They do not enable flow in the opposite direction even under a no-power condition. Thus, the three port two way check valve of the present invention is wisely installed downstream from the pump and a bypass line around the pump connects upstream of the pump. This enables the pump to operate in the intended fashion when it is powered. This enables flow in the opposite direction past the pump without damaging the pump.
Other circumstances can be imagined where a three port two way check valve is most helpful. The apparatus of the present invention is particularly adapted for use in such circumstances. The valve of the present invention is especially economical in comparison with valves known in the prior art. This valve is relatively inexpensive to manufacture. The cost of manufacture is reduced by using a standard fabricated tee of the necessary size. The tee is adapted to connection to the three pipe lines by welding standard flange plates to it, typically those in accordance with API standards. This assembles the entire body of the apparatus. Moreover, a valve assembly is installed in two of the three ports. One is installed in the center port and a second valve element is installed in one of the two remaining ports. The valve assembly preferably includes an encircling valve seat and a valve element which is hinged to the seat. Fluid flow in one direction forces the valve element open, swinging about the hinge. Fluid flow in the opposite direction of course closes the valve element against the seat thereby providing the check valve function. The present invention uniquely provides the assurance that one valve member is closed when the other is open so that the check valve function is correctly observed.